I have never heard of feeding anything to a bull to make him want sex. A bull usually wants sex when the cow is ready. The cow puts off a scent, so the bull knows.
A healthy bull will not need any special feed to breed a cow. There are other techniques in breeding that envolve artificial insemination which is a different story. There is a product called Spanish Fly which will cause irritation to genitals. Maybe that is what you are thinking of. I doubt it is used any longer for animal breeding. The female has to be receptive non the less.
And why is it necessary?
